2011*

One of (many!) unpleasant implications of making the census long form voluntary is its effects on how data are tracked through time. Between censuses, Statistics Canada does the best it can to keep track of changes using survey data, but there's always the risk of sampling error accumulating as time goes on. The census - which in the past was not subject to sampling error - serves as an anchor for these higher-frequency series in order to produce data that can be compared across longer periods of time.

But 2011 will be different. Unless the federal government reverses its decision, researchers will be obliged to put an asterisk next to numbers from the 2011 census, with a footnote explaining that because these data were not calculated using the same methodology, they are not strictly comparable to previous numbers.

And since we're talking about using the census to look at long-run trends, here's a summary of the history of questions that have been asked since the first census in 1871 (copied from here). It's an awful lot of history to flush away.